Leadframes, air-cavity packages, and electronic devices with offset vent holes, and methods of their manufacture

Abstract

A leadframe (e.g., incorporated in a device package) includes a feature (e.g., a die pad or lead) with a vent hole formed between first and second opposed surfaces. The cross-sectional area of the vent hole varies substantially between the surfaces (e.g., the vent hole has a constricted portion). The vent hole may be formed from a first opening extending from the first surface toward the second surface to a first depth that is less than a thickness of the leadframe feature, and a second opening extending from the second surface toward the first surface to a second depth that is less than the thickness of the leadframe feature, but that is large enough for the second opening to intersect the first opening. Vertical central axes of the openings are horizontally offset from each other, and the constricted portion of the vent hole corresponds to the intersection of the openings.

What is claimed is: 
     
       1. A device comprising:
 a leadframe feature having a first surface, a second surface opposed to the first surface, and a vent hole formed between the first surface and the second surface, wherein a cross-sectional area of the vent hole varies substantially between the first surface and the second surface; and 
 molding compound partially encapsulating the leadframe feature, wherein the molding compound is not disposed within the vent hole. 
 
     
     
       2. The device of  claim 1 , wherein the vent hole has a constricted portion between the first surface and the second surface, and wherein a first cross-sectional area of the vent hole at the constricted portion is in a range from 10 to 90 percent of a second cross-sectional area at the first surface. 
     
     
       3. The device of  claim 2 , wherein the first cross-sectional area is in a range from 25 to 90 percent of the second cross-sectional area. 
     
     
       4. The device of  claim 3 , wherein the first cross-sectional area is in a range from 50 to 90 percent of the second cross-sectional area. 
     
     
       5. The device of  claim 1 , wherein the vent hole comprises:
 a first opening extending from the first surface toward the second surface to a first depth that is less than a thickness of the leadframe feature; and 
 a second opening extending from the second surface toward the first surface to a second depth that is less than the thickness of the leadframe feature, but that is large enough for the second opening to intersect the first opening, wherein a vertical central axis of the first opening and a vertical central axis of the second opening are horizontally offset from each other by a distance in a range from 10 to 90 percent of a diameter of the first opening, and wherein a constricted portion of the vent hole corresponds to an intersection of the first opening and the second opening. 
 
     
     
       6. The device of  claim 5 , wherein the vertical central axis of the first opening and the vertical central axis of the second opening are horizontally offset from each other by a distance in a range from 25 to 75 percent of the diameter of the first opening. 
     
     
       7. The device of  claim 5 , wherein the vertical central axis of the first opening and the vertical central axis of the second opening are horizontally offset from each other by a distance in a range from 50 to 90 percent of the diameter of the first opening. 
     
     
       8. The device of  claim 5 , wherein the first depth and the second depth each are in a range of 25 to 75 percent of the thickness of the leadframe feature. 
     
     
       9. The device of  claim 1 , wherein the leadframe feature is a lead having an elongated shape, and wherein with a first portion of the lead is oriented toward a die pad, a second portion of the lead is oriented away from the die pad, and a central portion of the lead extends between the first portion and the second portion, and wherein the vent hole is formed through the first portion of the lead. 
     
     
       10. The device of  claim 1 , wherein the leadframe feature is a die pad. 
     
     
       11. The device of  claim 1 , further comprising:
 fill material that seals the vent hole. 
 
     
     
       12. A device comprising:
 a leadframe feature having a first surface, a second surface opposed to the first surface, and a vent hole formed between the first surface and the second surface, wherein a cross-sectional area of the vent hole varies substantially between the first surface and the second surface; and 
 a lid having a surface permanently coupled to the device, wherein the lid partially defines an air cavity, and wherein the vent hole allows airflow between the air cavity and an exterior of the device during a lid attach process. 
 
     
     
       13. A device comprising:
 a leadframe feature having a first surface, a second surface opposed to the first surface, and a vent hole formed between the first surface and the second surface, wherein a cross-sectional area of the vent hole varies substantially between the first surface and the second surface; and 
 fill material that seals the vent hole, wherein the fill material comprises solder. 
 
     
     
       14. A device comprising:
 a leadframe feature having a first surface, a second surface opposed to the first surface, and a vent hole formed between the first surface and the second surface, wherein a cross-sectional area of the vent hole varies substantially between the first surface and the second surface, wherein the leadframe feature is selected from a substantially planar die pad, and a lead of a plurality of leads that are located around a perimeter of the die pad; and 
 molding compound partially encapsulating the die pad and the plurality of leads, wherein a combination of the die pad, the plurality of leads, and the molding compound form a package base. 
 
     
     
       15. A method comprising:
 forming a vent hole between a first surface and a second surface of a leadframe feature, wherein the vent hole is formed so that a cross-sectional area of the vent hole varies substantially between the first surface and the second surface; and 
 partially encapsulating the leadframe feature with molding compound, wherein the molding compound is not disposed within the vent hole. 
 
     
     
       16. The method of  claim 15 , wherein forming the vent hole comprises:
 forming a first opening extending from the first surface toward the second surface to a first depth that is less than a thickness of the leadframe feature; and 
 forming a second opening extending from the second surface toward the first surface to a second depth that is less than the thickness of the leadframe feature, but that is large enough for the second opening to intersect the first opening, wherein a vertical central axis of the first opening and a vertical central axis of the second opening are horizontally offset from each other by a distance in a range from 10 to 90 percent of a diameter of the first opening, and wherein a constricted portion of the vent hole corresponds to an intersection of the first opening and the second opening. 
 
     
     
       17. A method comprising:
 forming a vent hole between a first surface and a second surface of a leadframe feature, wherein the vent hole is formed so that a cross-sectional area of the vent hole varies substantially between the first surface and the second surface, wherein the leadframe feature is selected from a substantially planar die pad, and a lead of a plurality of leads that are located around a perimeter of the die pad; 
 partially encapsulating the die pad and the plurality of leads with molding compound, wherein a combination of the die pad, the plurality of leads, and the molding compound form a package base; 
 attaching one or more die to the die pad; 
 forming electrical connections between the one or more die and the plurality of leads; 
 performing a lid attach process to attach a lid to the package base over the one or more die, wherein a top surface of the package base and an interior surface of the lid define an air cavity, and wherein the vent hole remains open during the lid attach process; and 
 closing the vent hole after the lid attach process in order to seal the air cavity.